Dementia of the Alzheimer type and Parkinson's disease are brain dysfunctions caused by degeneration or loss of neurons. Dementia of the Alzheimer type have been treated by using anticholinesterases or muscarinic receptor agonist. Parkinson's disease has been treated by administration of dopamine or dopamine agonist. Although the symptoms are temporarily improved by the treatments using such drugs, progress of the pathological conditions could be neither stopped nor retarded.
Motor paralysis is a disease wherein voluntary movement is inhibited by the dysfunction of motor nerve extending from the motor center to the muscle. The motor paralysis caused by the dysfunction of the upper motor nerve extending from the cerebrum to the anterior horn cell is called central paralysis, and the motor paralysis caused by the dysfunction of the lower motor nerve extending from the anterior horn cell to muscle is called peripheral paralysis. Motor paralysis is divided into monoplegia (paralysis of a single limb), hemiplegia (paralysis of upper and lower limbs on one side of the body), paraplegia (paralysis of both lower limbs), and quadriplegia depending on the paralyzed part. Although various treatments (such as rehabilitation and neural transplantation) corresponding to individual symptoms have been conducted, there is so far no therapeutic drug that is capable of regenerating the damaged neuron.
Use of a neurotrophic factor such as nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF) for the prevention or treatment of such diseases may be contemplated. These factors, however, are peptides with high molecular weight, and they are easily decomposed in the living body, and also, they are unable to pass the blood-brain barrier. Accordingly, these factors are strictly limited in their administration route.
In view of the situation as described above, an object of the present invention is to provide a compound which has a sufficiently low molecular weight so that the compound can pass the blood-brain barrier, and which is capable of repairing and regenerating the degenerated or lost neurons to thereby improve various neuropathies.